Conventionally, the magnetic tape is widely used as a recording medium for recording/reproducing data. As shown in FIG. 4, magnetic tape MT includes many data tracks DT where data is recorded formed in the width direction (the vertical direction in the drawing) of the magnetic tape MT in order to heighten storage density per unit area. In FIG. 4, four data tracks DT are formed. In addition, although not shown, the data tracks are subdivided by further two or more tracks, respectively. And in recent years, in order to make storage density per unit area still higher, width of each data track DT is narrowed and the number of the data tracks DT is increased.
However, when width of the data tracks DT is narrowed, minute movement of the magnetic tape MT in the width direction is repeated for various reasons during traveling. Therefore, it becomes difficult for magnetic disk recording and reproducing head (not shown) to trace the data track DT completely at the time of record/reproduction of data. So, in this kind of device that records/reproduces the magnetic tape for high-density record, the position of the magnetic disk recording and reproducing head to magnetic tape is dynamically controlled on the basis of the servo signal written on the magnetic tape beforehand at the time of record/reproduction of data. Namely, the servo signal is read by the magnetic disk recording and reproducing head, which is integrally formed with recording/reproducing head, and position offset of the magnetic disk recording and reproducing head in the width direction of the magnetic tape is detected, and the magnetic disk recording and reproducing head is moved so that this position offset may be corrected. In addition, the servo signal is written by the servo writer of exclusive use along the run direction (the direction of arrow A in the drawing) of the magnetic tape MT beforehand. In FIG. 4, four servo tracks ST are formed.
FIG. 5 is a conceptional view in elevation showing the conventional servo writer. As shown in FIG. 5, the conventional servo writer 20 includes feeding reel 21 that feeds out the magnetic tape MT where the servo signal is not written, writing head H1 that writes the servo signal on the magnetic tape MT fed out from the feeding reel 21, inspection head H2 formed on the downstream side of the writing head H1, and reads the servo signal written on the magnetic tape MT for inspection, and take-up reel 22 which takes up the magnetic tape MT in which the servo signal is written. Moreover, signs 23 and 24 are the capstan rollers that cause the magnetic tape MT run.
In the conventional servo writer 20 constituted as described above, the servo signal is written on the magnetic tape MT by supplying record current, which is a writing signal of servo pattern and by giving magnetism to the predetermined part of the magnetic tape MT. To be explained in detail, magnetism is given to the predetermined part of the magnetic tape MT by the writing head H1, and a predetermined part is magnetized, to thereby the servo pattern is formed on the magnetic tape MT. In addition, since the magnetic tape of the same kind is manufactured for a long period of time, the magnetic tapes of many kinds exist at the same period. Therefore, generally writing a servo signal on the magnetic tapes of many kinds by one set of a servo writer is performed.
If there are too few amounts of record current supplied to the writing head H1 in case a servo signal is written on magnetic tape MT, the predetermined part of magnetic tape MT is not fully magnetized. Therefore, correct writing of the servo signal is not allowed. Moreover, if the amount of record current supplied to the writing head H1 is too large, the area beyond necessity is magnetized. Therefore, correct recording of the servo signal is not allowed. In addition, the thickness of a magnetic layer and the anti-magnetism of the magnetic layer change according to the kinds of the magnetic tape MT. The ranges of the amount of record current capable of writing the servo signal correctly differ for every kind of the magnetic tape MT. Therefore, in order to write the servo signal on the magnetic tape MT correctly, it is necessary to adjust the amount of record current supplied to the writing head H1 for every kind of the magnetic tape MT.
However, in the conventional servo writer 20 as shown in FIG. 5, when writing the servo signal in many kinds of magnetic tape MT, the amount of record current of the writing head H1 has to be adjusted by manual handling one by one for every kind of the magnetic tape MT. Therefore, low efficiency is caused.